var test = () => {
  var i
  var arr = ['vue', 'react', 'node']
  for (i = 0; i < arr.length; i++) {
    console.log(arr[i])
  }
}
test()


var test2 = () => {
  var i
  var arr = ['vue', 'react', 'node']
  var len = arr.length
  for (i = 0; i < len; i++) {
    console.log(arr[i])
  }
}
test2()

var test3 = () => {
  var arr = ['vue', 'react', 'node']
  var len = arr.length
  while(len--) {
    console.log(arr[len])
  }
}
test3()